[SourceKit] Support location info for macro-expanded Clang imports

Currently, when we jump-to-definition for decls that are macro-expanded
from Clang imported decls (e.g., safe overloads generated by
@_SwiftifyImport), setLocationInfo() emits a bongus location pointing to
a generated buffer, leading the IDE to try to jump to a file that does
not exist.

The root cause here is that setLocationInfo() calls getOriginalRange()
(earlier, getOriginalLocation()), which was not written to account for
such cases where a macro is generated from another generated buffer
whose kind is 'AttributeFromClang'.

This patch fixes setLocationInfo() with some refactoring:

-   getOriginalRange() is inlined into setLocationInfo(), so that the
    generated buffer-handling logic is localized to that function. This
    includes how it handles buffers generated for ReplacedFunctionBody.

-   getOriginalLocation() is used in a couple of other places that only
    care about macros expanded from the same buffer (so other generated
    buffers not not relevant). This "macro-chasing" logic is simplified
    and moved from ModuleDecl::getOriginalRange() to a free-standing
    function, getMacroUnexpandedRange() (there is no reason for it to be
    a method of ModuleDecl).

-   GeneratedSourceInfo now carries an extra ClangNode field, which is
    populated by getClangSwiftAttrSourceFile() when constructing
    a generated buffer for an 'AttributeFromClang'. This could probably
    be union'ed with one or more of the other fields in the future.

rdar://151020332
(cherry picked from commit 44aba1382d)

lib/AST/Module.cpp

@@ -68,6 +68,7 @@
 #include "llvm/Support/SaveAndRestore.h"
 #include "llvm/Support/YAMLTraits.h"
 #include "llvm/Support/raw_ostream.h"
+#include <optional>
 
 using namespace swift;
 
@@ -847,49 +848,6 @@ SourceFile *ModuleDecl::getSourceFileContainingLocation(SourceLoc loc) {
   return nullptr;
 }
 
-std::pair<unsigned, SourceRange>
-ModuleDecl::getOriginalRange(SourceRange range) const {
-  assert(range.isValid());
-
-  SourceManager &SM = getASTContext().SourceMgr;
-  unsigned bufferID = SM.findBufferContainingLoc(range.Start);
-
-  auto startRange = range;
-  unsigned startBufferID = bufferID;
-  while (const GeneratedSourceInfo *info =
-             SM.getGeneratedSourceInfo(bufferID)) {
-    switch (info->kind) {
-#define MACRO_ROLE(Name, Description)  \
-    case GeneratedSourceInfo::Name##MacroExpansion:
-#include "swift/Basic/MacroRoles.def"
-    {
-      // Location was within a macro expansion, return the expansion site, not
-      // the insertion location.
-      if (info->attachedMacroCustomAttr) {
-        range = info->attachedMacroCustomAttr->getRange();
-      } else {
-        ASTNode expansionNode = ASTNode::getFromOpaqueValue(info->astNode);
-        range = expansionNode.getSourceRange();
-      }
-      bufferID = SM.findBufferContainingLoc(range.Start);
-      break;
-    }
-    case GeneratedSourceInfo::DefaultArgument:
-      // No original location as it's not actually in any source file
-    case GeneratedSourceInfo::ReplacedFunctionBody:
-      // There's not really any "original" location for locations within
-      // replaced function bodies. The body is actually different code to the
-      // original file.
-    case GeneratedSourceInfo::PrettyPrinted:
-    case GeneratedSourceInfo::AttributeFromClang:
-      // No original location, return the original buffer/location
-      return {startBufferID, startRange};
-    }
-  }
-
-  return {bufferID, range};
-}
-
 ArrayRef<SourceFile *>
 PrimarySourceFilesRequest::evaluate(Evaluator &evaluator,
                                     ModuleDecl *mod) const {
@@ -1431,11 +1389,11 @@ SourceFile::getExternalRawLocsForDecl(const Decl *D) const {
   bool InGeneratedBuffer =
       !SM.rangeContainsTokenLoc(SM.getRangeForBuffer(BufferID), MainLoc);
   if (InGeneratedBuffer) {
-    unsigned UnderlyingBufferID;
-    std::tie(UnderlyingBufferID, MainLoc) =
-        D->getModuleContext()->getOriginalLocation(MainLoc);
-    if (BufferID != UnderlyingBufferID)
-      return std::nullopt;
+    if (auto R = getUnexpandedMacroRange(SM, MainLoc)) {
+      if (BufferID != SM.findBufferContainingLoc(R.Start))
+        return std::nullopt;
+      MainLoc = R.Start;
+    }
   }
 
   auto setLoc = [&](ExternalSourceLocs::RawLoc &RawLoc, SourceLoc Loc) {